SPERMATOGENESIS IN THE ALBINO RAT 155 



Cytoplasmic structures 



A chromatoid body has been mentioned on p. 151. This is a 

 lightly staining mass with chromatin reaction, very small and 

 apparently spherical (figs. 19, 20 and 23). Its first positive' 

 appearance is in the late prophase stages of the first spermato- 

 cytes after the disappearance of the nuclear membrane. At first 

 it appears to be near the chromosomes, but at later stages it is 

 always found well out in the cytoplasm. In some metaphase 

 cells it is doubled. It is lost during the anaphase of the first 

 spermatocytes and during the interkinesis stage, but reappears 

 in the second spermatocyctes.. Nothing of equivalent form is 

 found in the spermatids. In these cells, however, there is a mass 

 lying near the nucleus which stains like chromatin. It develops 

 intensity of staining reaction as the spermatids advance in differ- 

 entiation. In its fuller development it is seen in figure 1, Sptd. 

 3, where it appears as a globular body, but much larger and stain- 

 ing more deeply than the chromatoid body. In the same figure 

 it is shown less developed in Sptd. 1. See page 169 for further 

 discussion. 



4. DISCUSSION 



The points which need discussion are chiefly the following: 

 the number of chromosomes, the accessory, the constitution of 

 the first spermatocyte chromosomes, the differentiation of sper- 

 matogonia and Sertoli cells, the age when spermatozoa are mature, 

 and cytoplasmic phenomena. The first two topics will be con- 

 sidered together. 



The number of chromosomes and the accessory 



Duesberg ('08) is the first observer to record a chromosome 

 count for the rat. He is uncertain about the number, but places 

 it at probably 24 in the spermatogonia and 12 in the first 

 spermatocytes. It seems strange that he and I should differ 

 so widely in this respect. There is apparently no question 

 about the species of the rat, as we both used Mus norwegicus, 

 var. alb. An accessory is not mentioned by him. 



